Malignant external otitis (MEO) is a rare infection of the temporal bone primarily affecting elderly patients and diabetics or immunocompromised individuals, which may have dismal prognosis if treatment is not prompt and adequate. Almost 95% of MEO cases reported in the literature are attributed to Pseudomonas aeruginosa, and this pathogen is isolated from aural drainage in > 90% of cases. However, in recent years fungal and polymicrobial temporal bone infections have been reported with increasing frequency. The aim of this paper is to discuss a possible pitfall in MEO treatment using an unusual clinical case. In this patient, bacteriological data positive for Pseudomonas delayed correct diagnosis of Aspergillus infection, which was obtained after surgical debridement and biopsy of the infra-temporal space.